Wooster Geologists

Mark Wilson August 9th, 2009

FIELD, BRITISH COLUMBIA, CANADA–Our study group was fortunate to meet Whitey Hagadorn (Amherst College and Denver Museum of Natural History) and Sally Walker (University of Georgia) for a hike to an exposure of stromatolites in the Pika Formation (Middle Cambrian) near Lake Helen and Lake Katherine in Banff National Park. A stromatolite is a finely-laminated sedimentary rock produced by mats of cyanobacteria in a shallow sea collecting and trapping thin layers of sediment. They are relatively common features in Precambrian sediments (the oldest of fossils, in fact) and become significantly more rare in younger rocks (although they are still around today). These Cambrian stromatolites are interesting because of what they can tell us about Cambrian marine conditions, including tidal dynamics, bioturbation, and grazing herbivore pressures.

Stromatolites exposed as domal structures in this eroding outcrop of the Pika Formation (Middle Cambrian) above Helen Lake in Banff National Park.

A natural cross-section of the Pika Formation stromatolites showing their laminated nature and sediment which has accumulated around their heads.

A hardground (light unit) exposed in cross-section in the sediment between stromatolite heads. This is a layer of carbonate sediment which was cemented on the seafloor and then eroded by currents. The dark sediment was deposited later on top of the scoured surface. The hardground layer had been previously burrowed when still soft.

Beautiful folds in the rocks above the Pika Formation stromatolites. They are nearly recumbent in some parts. I'll leave their interpretation to my structural geology colleagues Sam Root and Shelley Judge!

A marmot on the banks of Helen Lake. Not at all camera shy, this little guy.

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Mark Wilson June 17th, 2009

I was very impressed by the Ordovician rocks I saw in the Leningrad Region on this past trip.  I had seen parts of the Ordovician System in Estonia nearby, but not to this extent nor this particular facies.  My model for Ordovician rocks had been based too strictly on those I’ve worked with in North America.  Now I realize that the environmental conditions and faunas were significantly different on the ancient continent of Baltica — enough to produce unexpected trace fossils, especially on and in the hardgrounds.  My perspective was changed, and thus the kinds of questions my students and I will be addressing in the next few years.

Nikolai, Sergei, Andrei, me, and my host Andrey in the Sablino Mines. I really don't know why there was a decorated Christmas tree in this cavern.

My Russian host, Andrey Dronov, was extremely generous and patient, freely sharing with me his scientific thoughts and his passion for Russian history and culture.  I could not have asked for better.  Remarkably, I met him for the first time on this expedition.  My other Russian colleagues were great fun, and they also taught me much about Russia and its geology.

I learned that field geology in Russia is difficult and certainly could not be done without a knowledgeable Russian host.  Every outcrop was farther, muddier, steeper and more overgrown than I expected.  In fact, we looked at outcrops American geologists would have given up on years ago.  If the rocks were there, we found them by hacking through the vegetation and digging them out with shovels.

Do you see the outcrops of limestone along these banks of the Lynna River? Neither do I. They are there, though, and Andrey and I found them with an epic jungle journey on our last field day.

The major catch to doing Independent Study work in Russia for a student is that we could not take specimens back to Wooster.  We could, though, work in the geological lab facilities at the Academy of Sciences in Moscow, collecting enough data and images to keep a student busy for a year back home.  I would look forward to showing a student these unusual rocks and fossils, and I now know how better to prepare for work in Russia!

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Mark Wilson June 8th, 2009

BABINO, LENINGRAD REGION, RUSSIA–Today we visited an active quarry, which is a different experience from the riverbank exposures and abandoned quarries we have been frequenting.  Quarry mud has a special character — a kind of purified mud, the kind of mud all mud aspires to be.  There are also very large trucks splashing by, giant rock saws whining, cranes lifting large blocks, and small groups of curious workmen who want to see what we are doing there with our hammers that now seem so small.  Active quarries can produce the very best exposures for geologists, especially those interested in the boundaries between rock units as we are.  This quarry at Babino N60.03035°, E32.38613°) is particularly good because they quarry Ordovician limestone by first cutting it vertically, and then lifting the rocks away in sections, revealing smooth surfaces perpendicular to bedding.

Cut surface through Ordovician section, Babino Quarry.

I want most to see the boundary between the Lower and Middle Ordovician rocks, and look at the trace fossils above and below it.  This boundary — a plane in the rocks which extends across northeastern Russia, Scandinavia, and parts of northern Europe — could not be better displayed than the way we saw it here.  It is an erosional surface which has been cemented into a carbonate hardground and then bored (to some extent that we are debating) and abraded smooth.  Above it is a significant change in the fossil fauna, a change which can be seen around the world.  In no place is this boundary better presented to geologists than here.

Lower/Middle Ordovician boundary in the Babino Quarry.

The trace fossils along this boundary are complex and may show both boring and burrowing behavior.  The distinction depends on when the sediments were soft, firm and cemented, and on the varieties of organisms which did the work.

Borings in the Lower/Middle Ordovician boundary at Babino Quarry.

I can’t take these specimens home for further examination.  I’d very much like to make thin-sections (slices of rock shaved down until almost transparent for microscopic analysis) of all the critical intersections, but that will have to wait.  Andrey collected many samples he can cut up and share from his lab in Moscow.

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Mark Wilson June 7th, 2009

SASS RIVER, LENINGRAD REGION, RUSSIA–The main geological attractions for me on this expedition are the abundant carbonate hardgrounds in the Lower and Middle Ordovician in this part of the world.  A carbonate hardground is a cemented seafloor.  What were soft sediments on the bottom were cemented with carbonate minerals (calcite in the Ordovician) so that they became a rocky surface several centimeters thick.  The sediment is usually carbonate mud and shells, so the result is essentially a limestone seafloor.  Many invertebrate animals colonize these hard surfaces by wither encrusting them or boring into them.  Those eocrinoids illustrated earlier, for example, often encrusted Early and Middle Ordovician hardgrounds.

Today at the Sass River Carbonate Mound locality (N60.02316°, E32.62471°) we saw numerous hardgrounds bored by a shallow variety of a trace fossil called Trypanites.

Borings in Ordovician hardground fragments.

These are the most common borings in hardgrounds.  This particular type of Trypanites is remarkably shallow — often appearing as pits rather than the usual penetrating cylinder.  Another difference between these hardground fossil faunas and those I know best in North America and western Europe.

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